Precast concrete panels are being used for a variety of application in building construction owing to savings obtained from reductions in construction time and forming requirements. Precast panels are normally prepared by casting them in suitable molds on a horizontal surface, which may be an already cast floor slab at the construction site. Upon curing, the panels are placed in vertical position by means of a crane using "tilt-up" construction techniques and are bolted in place. One type of panel which has gained widespread acceptance is a waffle-shaped panel in which weight savings are obtained, consistent with high strength, by providing a network of intersecting reinforced ribs projecting outward from one face of the panel. The ribs are cast integrally with the remainder of the panel using a special mold. Typically, a panel having the strength of an eight-inch structural section may be obtained using the equivalent of only three and one-half inches of concrete.
Various disadvantages and limitations are exhibited by existing waffle-shaped panels. The as-cast panels are not insulated, and if insulation is to be provided, it must be installed later, typically by inserting fiberglass batts into the voids between the ribs and enclosing the batts by attaching an insulating foam board to the rib ends. Other measures such as attaching a foam board on the flat panel face with an adhesive or nailing furring strips to the panel rib ends with concrete nails have also been used. Such measures are laborintensive and add substantially to costs. In addition, the existing panels have been limited in their application for use as ceiling panels owing to their inability to meet strength requirements for long overhead spans.